Question

I was wondering (there has to be an easy solution) if there is a way to make a number of objects, and use them in other classes and objects from those classes, without having to update them (in Java). An example:

Class A, B and C make objects a b and c.
Then I have class D, which makes object d.
Now I want to use d in a, change it, use d in b, change it there and use d in c and still have all the changes from a and b.
I know it’s possible with using d as an argument in the functions, and returning d, but that is not useful in the program I’m making at the moment.

Any help?

Ok, My example in code:

public class A {
   D d = new D ();
   A(D dObject){
     this.d = dObject;
   }
   public void add () {
     DObject.add(5);
   }
}

public class B {
   D d = new D ();
   B(D dObject){
     this.d = dObject;
   }
   public void add () {
     DObject.add(5);
   }
}

public class C {
   D d = new D ();
   C(D dObject){
     this.d = dObject;
   }
   public void add () {
     DObject.add(5);
   }
}
public class D {
   public int x=0;
   public void add (int y){
      x +=y;
   }
}

// in main class:
D d = new D();
A a = new A(d);
B b = new B(d);
C c = new C(d);

a.add();
b.add();
c.add();

// d.x should give 15 now. 

Answer 1

I’m not sure if I understand right – the code you posted does exactly what you say (d.x is 15), if you correct the syntax errors.

Here is a version that should work:

public class A {
   D d;
   A(D dObject){
     this.d = dObject;
   }
   public void add () {
     d.add(5);
   }
}

public class B {
   D d;
   B(D dObject){
     this.d = dObject;
   }
   public void add () {
     d.add(5);
   }
}

public class C {
   D d;
   C(D dObject){
     this.d = dObject;
   }
   public void add () {
     d.add(5);
   }
}
public class D {
   public int x=0;
   public void add (int y){
      x +=y;
   }
}

// in main class:
D d = new D();
A a = new A(d);
B b = new B(d);
C c = new C(d);

a.add();
b.add();
c.add();

// d.x should give 15 now. 

If you want d to stay the same instead of changing (e.g. d.x == 0 at the end), you can do one of these:

• make clones of the parameter dObject in the constructor of A, B, C, so each has its own D object.
• make D immutable and let its add method instead return a new D object. The add method of A, B, C would then have the implementation d = d.add(5);.